Recent developments in hand-held electronic devices such as mobile phones have resulted in improvements in the quality of sound reproduction, thereby enabling music to be played though such devices. Conventionally, it is common for the sound to be reproduced through headphones and an internally mounted loudspeaker is used only to produce general sounds such as ring-tones and other individual tones to signify key-presses. However, these devices are increasingly being provided with internal loudspeakers that can be used to project sounds/music directly from the device towards the listener in a hands-free format in addition to ring-tones and other more general sounds relating to the operation of the device. It will be appreciated that, if an internal loudspeaker is used to enable a user to listen to music, the quality of sound reproduction becomes an important consideration.
To maximise quality, it is desirable to be able to reproduce stereo effect sound to give the listener a greater 3-D or ‘spatial’ effect of the projected sound. However, producing stereo sound from a device as small as a mobile phone presents a number of problems. Firstly, two separate loudspeakers are required and, when the device is orientated in a position of use, the loudspeakers must be spaced horizontally from each other by a minimum distance so that sound is directed to either side of the listener to effectively reproduce a stereo effect. As mobile telecommunication devices are relatively small, obtaining the minimum horizontal spacing between the loudspeakers is difficult. However, if suitable digital processing is used, it is possible to spatially enhance the sound to expand the sound stage dramatically and produce a stereo effect.
The requirement for a minimum horizontal spacing between loudspeakers so as to direct sound towards either side of a listener leads to a problem when the device is intended for use in both an upright or ‘portrait’ position and also in a sideways or ‘landscape’ position. These two positions are illustrated by schematic front views of a prior art mobile device 10 comprising a mobile phone, shown in FIGS. 1A and 1B. When the phone 10 is being used, it is intended that it will be placed so as to face the listener in one of these positions. The ‘landscape’ position may be preferable, for example, when the user is also viewing information displayed on the screen in a landscape orientation, at the same time as listening to sound as the screen may be rectangular, as opposed to square in shape and the information or picture displayed may be viewed more easily in a landscape orientation. It can be seen that the phone 10 is rotated through an angle of 90 degrees between these two positions. The mobile phone 10, shown in the portrait position in FIG. 1A, has a left loudspeaker 12 and a right loudspeaker 14, separated from each other by a horizontal spacing Hp which is sufficient to enable spatial enhancement and reproduction of stereo sound. However, the mobile phone 10 is shown rotated clockwise by 90 degrees (see arrow A) into the landscape position in FIG. 1B and the loudspeaker 12 is now located directly above the loudspeaker 14. This means that the horizontal spacing of the two loudspeakers 12, 14 in the landscape position H1, is reduced to zero, so that they provide no spatial effect, thereby rendering production of stereo sound impossible. An example of a device of this type is known from U.S. Pat. No. 6,760,447 (P. A. Nelson et al).
One solution to the problem referred to above is to provide a first pair of loudspeakers spaced from each other in the horizontal direction to provide stereo sound when the phone is in the portrait position, and a second pair of loudspeakers displaced from each other in a vertical direction perpendicular to the direction of displacement of the first pair of loudspeakers such that, when the phone is rotated into the landscape position, the second pair of loudspeakers are horizontally displaced from each other and are thereby able to produce stereo sound.
However, this prior art solution suffers from the drawback that two pairs of loudspeakers are required in the mobile phone, which in turn leads to increased production costs and an increase in the size of the device. An alternative solution could be to provide three loudspeakers in an ‘L’ formation to make up the two ‘pairs’ of loudspeakers in which one speaker would be used when the device is in the portrait position and also when the device is in the landscape position. However, this arrangement would also suffer the drawback that three loudspeakers would be required, again, leading to increased production costs and an increase in the size of the device.